In rhetoric, a rhetorical device or resource of language is a technique that an author or speaker uses to convey to the listener or reader a meaning with the goal of persuading the reader or listener towards considering a topic from a different perspective. While a rhetorical device may be used to evoke an emotional response in the audience (the reader[s] or listener[s]) there are other reasons to use a rhetorical device. In the end the goal of rhetoric is to persuade towards a particular frame of view or a particular course of action and so appropriate rhetoric devices are used to construct sentences designed both to make the audience receptive through emotional changes and to also provide a rational argument for the frame of view or course of action.

The use of irony in rhetoric is primarily to convey to the audience an incongruity that is often times used as a tool of humor in order to deprecate or ridicule an idea or course of action.

The use of metaphor in rhetoric is primarily to convey to the audience a new idea or meaning by linking it to an existing idea or meaning with which the audience is already familiar. By making the new appear to be linked to or a type of the old and familiar, the person using the metaphor hopes to help the audience understand the new.

An example of rhetorical device is this passage attributed to a speech by Abraham Lincoln about a political adversary in which Lincoln said that his adversary had "dived down deeper into the sea of knowledge and come up drier than any other man he knew".

This attributed quote uses a body of water as a metaphor for a body of knowledge with the ironical idea of someone who gained so little from his education that he achieved the impossible of jumping into a body of water and climbing back out without getting wet.